We had previously demonstrated the effectiveness of the nucleotide analog, cytosine arabinoside (ARA-C) to block replication of the JC viral DNA the etiologic agent for progressive multifocal leukoencephalopathy (PML). Concentrations of ARA-C used were not toxic to the human glial cells in culture. Sixty-five AIDS patients with biopsy proven PML (the laboratory confirms the diagnosis using in situ DNA hybridization to detect viral DNA) were enrolled in the study. Peripheral blood and cerebrospinal fluid was taken from these patients as treatment proceeds and tested for viral DNA. In several samples, the viral DNA was identified in the B lymphocyte population and not T cells. This observation is consistent with previous clinical samples of B cell infection in bone marrow and spleen. Fifteen patients were treated with ARA-C using intrathecal administration. Lumbar punctures were performed on this group. Samples were collected in a longitudinal study. PCR analysis of CSF samples revealed that 79% of the patients tested had JCV in their CSF at some time during the course of PML. In 4 cases, however, there was no evidence of JCV in their CSF during their treatment regime. These patients also did not have viral DNA in their blood. The study is now completed. The data are being evaluated. It does appear that the patients with no viral DNA in the CSF have an extended life span compared with the other groups. We had previously determined that JCV is able to infect stromal cells derived from human tonsillar tissue as well as human hematopoietic stem cells. These cells are CD34+ and will differentiate into a lymphoid lineage. CD34+ cells that differentiate toward a monocyte/macrophage lineage are not susceptible to JCV infection. We have established a firm link between lymphoid and glial cells in the pathogenesis of JCV infection leading to demyelination in the human brain. We have also screened over 50 tonsil tissues and found JCV DNA in 15% of these samples. The host range of JCV is also expanded to include a glioma cell line derived from neuroblastoma cells. JCV host range is now known to include cells of glial and B lymphocyte lineage. The molecular similarities of these cells for JCV gene expression directly correlated with the NF-1 family of DNA binding proteins which function for transcription. We have also made an NF-1 class of expressing cell line in a JCV non permissive host cell. The expression of NF-1/D class protein conveys permissiveness to infection.